An electrophoresis method using a capillary has been used for determining the base sequence and base length of DNA, etc.
One of light irradiation systems to a plurality of capillaries includes a multi-focus system described in Patent Literature 1. In this system, capillaries at one or both of the ends of a capillary array comprising a plurality of capillaries arranged on a plane substrate are irradiated with a laser light, the laser light crosses the capillary array while propagating adjacent capillaries successively, and emission of light generated at the capillary array is detected by a light detector. A sample containing DNA labeled by a fluorescent dye is introduced into the capillary and irradiated by the laser light so as to propagate a plurality of capillaries arranged in a row. Fluorescent dye-labeled DNA emits fluorescence by laser light irradiation of the capillaries. DNA of the sample introduced into each of the capillaries can be analyzed by measuring fluorescence from each of the capillaries. This is identical also in the analysis of proteins, etc.